1. Field of the Invention
The invention relates to an electroactive passivation layer for semiconductor components as well as to a method for its manufacture.
2. Description of Related Art
Discrete and integrated semiconductor components, particularly those used in MOS [metal oxide semiconductor] technology, are sensitive to disturbances caused by surface charges and therefore require, especially at the locations where p-n junctions appear at the surface, semiconductive electroactive passivation and protective layers. The following is required for such passivation layers:
(1) A favorable, electrical coupling of the layer to n- and p-conducting active substrates must be possible without any blocking layer effects. In other words, small barriers and consequently high blocking currents (ohmic contacts) must be present. This requirement means a high defect concentration in the band gap and a sufficiently intrinsic conductivity provided by a hopping mechanism or an optical mobility gap of between 1.1 and 1.4 eV, allowing a sufficient number of charge carriers to be generated thermally.
(2) The electrical conductivity (at room temperature) must lie below 10.sup.-8 .OMEGA..sup.-1.cm.sup.-1, so that parasitic surface currents remain smaller than blocking currents between p- and n- conducting areas of the semiconductor to be protected.
(3) An adequate screening effect must be provided to protect the n- and p-conducting parts of the semiconductor. For this purpose,--besides a high density of rechargeable states (up to several 10.sup.19 cm.sup.-3.eV.sup.-1)--the protective and passivation layers must above all exhibit a low draft mobility of the charges.
(4) The passivation layers must be free of pinholes, have a low permeation coefficient for hydrogen and water, as well as offer mechanical and moisture protection.
(5) When the semiconductor components are heated--in the production process--to 290.degree. C., the passivation layers must not give off hydrogen.
Layers made of amorphous silicon (a-Si) are currently used as electroactive passivation layers for semiconductor components. These layers can be grown on the semiconductor components, however, the silicon can also be vapor-deposited, whereby the vapor-deposited layer is then tempered (see U.S. Pat. No. 4,322,452. The passivation layers can contain dopants, such as boron, phosphorus and aluminum, which allow the specific electrical resistance to be adjusted.
Electroactive passivation layers made of a-Si do contain a sufficient amount of defect (hole) states in the band gap. The required resistance value of about 10.sup.8 .OMEGA..cm can be adjusted through the deposition and sintering conditions, and doping only has a weak effect due to the high density of states. A serious disadvantage with these layers, however, is that their ability to be coupled to p-conductive substrates is considerably less than their ability to be coupled to n-conductive substrates. This can lead to surface openings on pn-junctions with high-blocking capability. Also, in the case of a-Si layers, the optical mobility gap can hardly be varied and thus cannot be adapted to any arbitrary active substrates. These layers are also particularly disadvantageous because of their lack of stability vis-a-vis moisture, ion diffusion, and mechanical influences.